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A reader named Mary recently contacted me with a question about eosinophilic granulomas (formerly known as rodent ulcers):

We adopted a beautiful 4-year-old tuxedo cat, Gunder, from the Humane Society. We were told that a mouth sore could be easily treated with Clavamox. I’ve spent two months getting him on a grain-free all-natural diet, which was recommended by the shelter vet. In addition, he has had a complete dental with two extractions and antibiotic treatment of gum inflammation. Although the sore is no longer ulcerated, it is still there, and varies day to day. It improved greatly when our vet gave him a cortisone shot, but we’ve had to wait for a second shot because of the oral/dental surgery. Do you have any suggestions regarding the next step?

Eosinophilic granulomas are lesions (sores or ulcers) that develop most frequently in and around the mouth, although they also can form on the feet, abdomen, thighs, and other parts of the body. They were originally called rodent ulcers because it was believed (wrongly) that they were the result of cats being bitten by prey animals during capture and consumption. The lesions have also been referred to as eosinophilic granuloma complex, and now a movement is under way to change the name to feline eosinophilic disease.

Any time experts can’t agree on a name for a syndrome, you can bet they don’t completely understand it. That certainly is the case for eosinophilic granulomas.

Here’s what we do know. They are not caused by rodent bites but are modulated by the immune system, and are likely related to (and often occur concurrently with) allergies. They are very painful and can markedly affect cats’ temperaments (one of the most fractious cats I’ve ever met became a total sweetheart when her condition was brought under control). Sadly, that can be devilishly hard to do.

Treatment most commonly involves removing potential immune system stimulators and administering medications to blunt the activity of the immune system.

Fleas are by far the most frequent triggers when cats suffer from overactivity of the immune system. Therefore, any cat with eosinophilic granulomas should be on a good flea preventative regardless of whether fleas are seen. Because a single flea bite here and there may exacerbate the problem, all other pets in the house also should receive flea prevention.

Food allergies may contribute. Cats are rarely allergic to grains — it is meat proteins that most often provoke allergy. Therefore, a grain-free diet may not help, but a change to a “novel protein” diet might make a difference. It’s worth talking to your vet about that.

Mosquito bites are believed to contribute to the condition in some cats. I’d recommend keeping your cat indoors and making sure that none of your window screens have holes in them.

Be aware that a period of several months without immune system stimulation may be necessary before results occur. Also, taking the steps above is not guaranteed to work — some cats will have persistent lesions even when their owners follow the recommendations.

Many medications are used to treat eosinophilic granulomas. Most of them are steroids related to cortisone. Although cats tolerate cortisone-type drugs quite well, I recommend using them as sparingly as possible to control symptoms while you work to remove immune system triggers from Gunder’s life. If a steroid helps to heal the lesion completely, it may be possible to prevent recurrence with very low doses of the medication.

Cyclosporine, a nonsteroid medicine that dampens the immune system’s response, is frequently successful in treating eosinophilic granulomas. It has been used in cats receiving transplanted kidneys, and also seems to be a good option for lesions that require long-term medication.

Antibiotics such as Clavamox do not treat eosinophilc granulomas, but they do help to alleviate infections that occur secondarily when opportunistic bacteria invade the lesions.

In addition to medications and allergen avoidance, physical treatments to remove or ablate eosinophilic granulomas sometimes are used. The lesions may be removed surgically, or treated with lasers, radiation, or cryotherapy. These physical treatments are not generally considered good first-line therapies, but they might be useful for persistent granulomas.

Finally, there is good news and bad news. First, the bad news. I am sorry to say that not all lesions that look like eosinophilic granulomas are, in fact, eosinophilic granulomas. Some other syndromes, most notably a cancer called lymphoma, may cause similar appearing lesions. A biopsy of the site can definitively determine the diagnosis.

And the good news: In my experience, stress sometimes contributes to eosinophilic granulomas. Living in a shelter and moving into a new home is notoriously stressful. There is a chance that Gunder’s newly stable lifestyle may help with the problem.

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